A wonder 
of nature, the lakes of Ounianga in the Sahara Desert have lasted thousands of years and have withstood dramatic climatic changes. Now, a German geologist has analyzed the sediments of the lake bed to shed light on a spectacular chapter in human history.
” Water ,” says Stefan Kröpelin, “water as far as the eye can see.” It points south, where there is only one thing that stretches towards the horizon : sand, sand, and more sand.
Kröpelin describes the reeds waving along the shore, the gazelles and giraffes drinking from the lake, and the hippos and crocodiles resting in its waters. But the desert before it is so inhospitable that it could hardly be home to more than a few dark beetles.
Kröpelin is not a fabulist . In fact, he knows what he’s talking about. A fertile and moist savannah once covered this region , where today not a single blade of grass grows.
The evidence is at Kröpelin’s feet. He has just detached some white pieces from the underlying bedrock with his geologist’s hammer. Using his hand , he collects dozens of small shells from the limestone. “Freshwater snails,” he says with satisfaction .
The geologist records the GPS coordinates in his blue field notebook. Then place the three pieces of rock in plastic bags and label them with a site number: “W 76”. Back home, at the Africa Research Center of the University of Cologne, you will determine the age of the rocks. “About 10,000 years,” he estimates . At least that was the age of the samples he took home after his last visit to this region of northern Chad.
The view to the north offers an idea of the lost paradise of which Kröpelin speaks. There, in a basin about 40 meters (131 ft) lower than the surrounding area, there is a lake lined with green vegetation . The huge sand dunes that reach the water like giant fingers will eventually bury the entire oasis, but now there are still date palms growing there.
The Lakes of Ounianga are a miracle of nature. These unusual green islands in a sea of sand have lasted thousands of years. There are no other comparable stretches of open water within a radius of more than 800 kilometers (500 miles).